Cigarette smoking is the leading cause of mortality in the U.S., resulting in over 480,000 deaths every year and costing more than $300 billion in loss of productivity. Smoking is also the leading cause of cancer and of deaths from cancer. Although the prevalence of smoking has declined over the past 50 years, large disparities in tobacco use remain across a number of groups. Latino/a smokers represent a major health disparity population in the U.S. and their unique healthcare needs are not being adequately addressed. Major contributing factors to smoking among Latinos in the U.S. include increased exposure to multiple stressors associated with crime and unemployment, elevated rates of anxiety/depression, discrimination, lack of Spanish-language treatments, and limited access to quality care. Although Latino smokers tend to smoke at lower rates than non-Latino Whites and are more likely than non-Latino White smokers to attempt cessation, they are less likely to receive in-person evidence-based care and more apt to fail in their quit attempts. Mobile technologies offer an ideal strategy to meet the widespread treatment needs of U.S. Latino/a smokers, as U.S. population data suggests that Latinos adopt smartphones at a rate higher than any other demographic group. However, there are currently no Spanish language mobile apps for Latino smokers that are psychosocial in nature and evidence-based for Latino smokers who often struggle with elevated rates of anxiety/depression and chronic exposure to life stressors (e.g., discrimination, acculturation). One cognitive- behavior therapy that is an ideal fit for this need and is particularly amenable to a mobile platform is anxiety sensitivity reduction-based smoking cessation. Anxiety sensitivity (AS) is a cognitive construct reflecting a disproportionate fear of anxiety-related sensations. Individuals with high AS interpret stress-related sensations (e.g., heart palpitations) as personally harmful or dangerous. There is a substantial literature linking AS to the development of anxiety and depressive disorders, PTSD, and substance use disorders. Moreover, AS is related to increased risk for smoking cessation failure and more severe withdrawal craving among smokers, including Latinos. Reducing AS prior to a quit attempt via cognitive restructuring and interoceptive exposure is related to increased success in quitting. Our team has previously adapted AS reduction for smoking in Spanish and results from this work suggest that a Spanish-language version of AS reduction for smoking cessation is effective for increasing smoking cessation success and reducing negative mood that impairs quit attempts. The aims of this Phase I application are to employ user centered design to develop and test the acceptability and efficacy of a Spanish language, mobile app, Impacto, which will incorporate proven AS reduction intervention strategies vs. a generic, Spanish language control smoking cessation app (Dejar de Fumar Asistente) in a small randomized controlled trial of adult Latino smokers. We expect that this project will result in a prototype of Impacto, whose clinical efficacy can then be tested in a fully-powered, Phase II randomized controlled trial.